INFLUENCE OF GRAIN-BOUNDARIES ON COMPLEX PERMEABILITY IN MNZN FERRITES

The permeability of ceramic soft magnetic ferrites distinctly depends on grain size. A model will be presented which accounts for this dependency in a quantitative fashion and without any adjustable parameter. This model involves boundary conditions for the spin system at the exchange-decoupled interfaces of adjacent grains and an inhomogeneous free energy density which brings the domain wall width as a natural length scale into the problem. It will be shown that this scale will precisely determine the grain size beyond which the permeability significantly starts to decrease.